In order to improve properties of various base materials, so far, it is a practice to form a vacuum-evaporated film on their surfaces by a plasma CVD method. In the field of packing materials, it is a known practice to improve the gas-barrier property by forming a vacuum-evaporated film on a plastic base material such as of a container by the plasma CVD method. For example, attempts have been made to improve the gas-barrier property by forming a vacuum-evaporated film of silicon oxide on the surface of a plastic container such as a polyethylene terephthalate (PET) bottle by the plasma CVD method by using a mixed gas of an organosilicon compound and oxygen as a reactive gas.
Here, attention has recently been given to a polylactic acid which is a representative example of a biodegradable plastic in a variety of fields from the standpoint of environmental problems, and bottles made from the polylactic acid have been put to the practical use in the field of packing materials, too. The bottles made from the polylactic acid have a gas-barrier property inferior to that of the PET bottles. Therefore, attempts have been made to improve properties such as gas-barrier property, etc. of the bottles made from the polylactic acid by forming a vacuum-evaporated film thereon.
Excellent gas-barrier property can be exhibited when a silicon oxide film is vacuum-evaporated on the PET bottles. However, various problems arouse when the silicon oxide film is vacuum-evaporated on a container made from such a resin as polylactic acid having a low glass transition point and a low heat resistance. That is, the polylactic acid has a glass transition point (Tg) of 58° C. and its heat resistance is inferior to that of PET (which has a Tg of, for example, 70° C.). That is, in order to obtain barrier property, the silicon oxide film must be vacuum-evaporated by using an oxygen gas and an organometal gas under a high-output condition (vacuum evaporation with a microwave output of, usually, not less than 600 W for 4 seconds or longer). Upon conducting the vacuum evaporation under the above high output condition, however, the bottle wall comprising the polylactic acid is thermally deformed or the wall surface is thermally deteriorated due to the heat of oxygen plasma or other plasma generated in the step of vacuum evaporation arousing such a problem that offensive odor generates in the bottle. Besides, the silicon oxide vacuum-evaporated film is hard and brittle, lacking flexibility, forming hydrophilic group such as silanol group, and cannot favorably follow the deformation of the polylactic acid basic material, cannot be closely adhered to the polylactic acid base material and, besides, has low barrier property against the water.
Vacuum-evaporated films of those other than the silicon oxide have also been studied extensively. For example, patent documents 1 and 2 are proposing hydrocarbon vacuum-evaporated films called diamond-like carbon films (DLC films) formed on the inner surface of a polylactic acid bottle. Further, patent document 3 proposes a polymer-like DLC film formed on the surface of a plastic container, the DLC film chiefly comprising amorphous carbon, and the CH3, CH2 and CH ratios in the film being 25%, 60% and 15%.    Patent document 1: JP-A-2001-18290    Patent document 2: JP-A-2005-14966    Patent document 3: JP-A-2006-131306